1. Field of the Invention
The present invention relates generally to the field of television systems and, more particularly, to a method and apparatus for digital television channel mapping.
2. Background Information
In analog television broadcasting, each broadcaster is assigned a physical channel. The physical channel identifies a unique frequency that is used by a broadcaster to embed television signals for transmission. Thus, there is a direct one-to-one relationship between the channel number selected on the television by the user and the actual frequency assigned to that channel.
In digital television, however, there is a many-to-many relationship between the channel selected on the television and the physical channel. Digital television is defined by Digital Television Standard, published in September of 1995 by the Advanced Television Systems Committee (ATSC) Standard (A/53) [hereinafter referred to as xe2x80x9cthe DTV Standardxe2x80x9d], the contents of which are fully incorporated herein by reference. A virtual channel is defined as having a major channel number and a minor channel number in the form X.Y where xe2x80x9cXxe2x80x9d is the major channel number and xe2x80x9cYxe2x80x9d is the minor channel number. By splitting a virtual channel into major and minor components, a broadcaster is allowed to maintain its channel identity, and at the same time provide multiple programs. Thus, a broadcaster can provide its analog programming on channel C (where xe2x80x9cCxe2x80x9d is a positive whole number), a first digital programming on channel C.1, a second digital programming on channel C.2, and so on. In digital television, broadcasters can map one or more major channels to one or more physical channels.
To facilitate the mapping of virtual channels to physical channels, each physical channel is assigned a unique Transport Stream Identifier (xe2x80x9cTSIDxe2x80x9d). The TSID is defined in Program and System Information Protocol for Terrestrial Broadcast and Cable, published in December of 1997 by the ATSC Standard (A/65) [hereinafter referred to as xe2x80x9cthe PSIP protocolxe2x80x9d], the contents of which are fully incorporated herein by reference. The PSIP protocol defines a Virtual Channel Table (VCT) that is transmitted for each physical channel. The TSID is contained as part of the header of the table. The DTV standard has a mapping mechanism that maps a virtual channel number with the TSID, and maps the TSID to the physical channel number in order to tune to the correct frequency.
However, there are drawbacks associated with the DTV standard in that the TSID information provided by one or more broadcasters may not be correct. First, the DTV standard allows for a situation where the same major channel can be mapped to different physical channels. For example, the DTV standard allows for virtual channel C.1 to be mapped to a first physical channel, and virtual channel C.2 to be mapped to a different physical channel. Second, two or more different major channels may be mapped to the same physical channel (e.g., both major channels C1 and C2 may be mapped to the same physical channel). This may occur when a broadcaster has extra bandwidth and shares the extra bandwidth with the public for public access. Third, in the typical case, one major channel is contained in one physical channel. However, the TSID used to map a given virtual channel number to a physical channel may not be reliable in that broadcasters may assign the same TSID to two different physical channels without consideration of collisions. In such a case, relying solely upon the TSID for tuning to a physical channel can lead to unpredictable results.
Accordingly, there is a need in the technology for a method and apparatus to overcome the aforementioned drawbacks.
The present invention is directed at a mapping method and apparatus for digital television channel mapping. In one embodiment, the method includes detecting a virtual channel selected by a user where the virtual channel is divided into major and minor channels, obtaining a first physical channel in a first mapping table that maps to the major channel, causing the first physical channel to be tuned, and collecting a first VCT from the first physical channel. The method further includes retrieving a first TTSID assigned to the first physical channel and a CTSID of the virtual channel from the first VCT, and decoding audio and video signals from the first physical channel if the first TTSID is equal to the CTSID.
Other embodiments are described and claimed herein.